Method for producing malleable and ductile beryllium bodies



- INVENTOR. Hmz/@Y M DUDAS ODUCING MALLEABLE AND RYLLIUM BODIES OriginalFiled Aug. 22, 1947 H. W. DODDS METHOD FOR PR DUCTILE BE ATTORNEY WTHDFR PRDUCING MALLEABLE AND DUCTILE BERYLLIUM BODIES Harry W. Dodds, BayVillage, Ghio, assigner, by mesne assignments, to the United States ofAmerica as represented by the United States Atomic Energy CommissionContinuation of abandoned application Serial No. 770,082, August 22,1947. This application February 23, 1955, Serial No. 491,103

8 Claims. (Cl. 75-225) The invention relates to a new and improvedmethod of producing bodies of metallic beryllium having desirablephysically properties which it has not been commercially feasible tosecure heretofore. This application is a continuation of my earlierfiled application Serial No. 770,082, filed August 22, 1947, nowabandoned.

It is an object of the invention to provide an improved method ofproducing bodies of beryllium which is capable of edecting purication ofthe constituent metal, of securing excellent physical propertiesincluding a finegrained heterogeneous structure, marked malleability,considerable ductility, machinability and insensitiveness to thermalshock, of providing control of the density of the metal up to itsmaximum theoretical density, and of producing very large bodies havingthe stated properties throughout.

Other objects of the invention incidental or vancillary to thoseindicated above will be apparent from the description which follows.

With the noted objects in view the invention, in its most importantaspect, consists in charging beryllium in a powdered state suitable forpowder metallurgy purposes into a container or die having a cavity ofthe form of the body to be produced and subjecting the powdered materialto a prolonged treatment in which it is subject simultaneously tovacuum, heating at a sintering temperature low enough to preventsubstantial grain growth in the metallic mass and mechanical pressuregreat enough to maintain the sintering charge in contact with thecontainer walls, with the effect of removal of impurities present,sintering and condensation to desired density of the powdered mass andconformation thereof to the container cavity. Preferably the containeror die of suitable strength is fitted with a thin-walled metal linerwhich facilitates the mechanical condensing of the charge as well as itsseparation from the die.

ln another aspect, the invention may include controlling 'the density ofthe sintered body produced in the above stated treatment by controllingthe weight of the charge of powdered material introduced into thetreating container, measuring reduction in volume of the treated chargefrom time to time while it is subject to the abovenoted vacuum, heat andpressure treatment and terminating the pressure and heating when thevolume of the charge is reduced to a predetermined value calculated inrelation to the weight of the charge.

ln order that the invention in its various aspects may be clearly andfully understood the procedure and the special apparatus preferred forthe practice of the invention will be described with reference to theaccompanying drawing.

1n the drawing,

Fig. 1 is a view, partly in side elevation and partly in centralvertical section, of a preferred form of apparatus.

Fig. 2 is a view on a larger scale of a sintering container in the formof a die suitable for use in the furnace of Fig. l to produce aberyllium gear wheel.

Ai O

rana Patented Dec. 31, 1957 The process of the present invention maystart with powdered metallic beryllium of technical grade from anyconvenient source. However, ordinary technical grade beryllium powdercontains a considerable amount of impurities, including flux material,slag, oxides and metals other than beryllium, and since it is desirablethat the powder have a minimum of such impurities it is desirable totake advantage of any economically feasible purification of the metallicberyllium to be used. In one such method, of a mechanical nature, theunpurified metallic beryllium is treated for removal of friable maerial,such as slag, by a series of crushing and screening operations whichleave the metal reduced to a particle size suitable for furtherreduction by grinding and screening.

Beryllium powder, whether produced by such a method of crushing,-grinding and screening or otherwise, may still contain some impuritiesand the present invention is designed to effect further purification ofthe metal, utilizing the furnace apparatus shown in the drawing.

This apparatus comprises a furnace having an opentopped structuredesignated generally'by the numeral 1 and comprising an outer metalshell 2 with a lining 3 of refractory material. 4 is a cover of similarmetal and refractory construction. Oil or gas-tired burners 5 mount# edin the side walls of the furnace serve to heat the interior chamberthereof. The furnace rests upon a suitable foundation comprising channelor I beams 6.

The treating chamber of the furnace generally designated by the numeral7 is formed by a steel tube it closed at its lower end by disc 9hermetically welded to the tube. The tube is flanged at its upper endand closed by cover plate 10. Chamber 7 is supported somewhat above thebottom of the furnace 1 on a refractory block 11 of heat insulatingmaterial. At its upper end the furnace tube 8 is fitted with an outletconduit 12 which is adapted to be connected to the intake of a vacuumpump (not shown) which may be of a conventional diffusion type toproduce a high vacuum.

A container 13 for the powdered material to be treated is shown in thetreating chamber 7 of the furnace. Container 13 comprises an open-toppedsteel pot 14 and a thin walled liner 15 of stainless steel which isremovably fitted in the cavity of the pot. The heavy walls of the potreinforce the liner so that it is adapted to sustain higher internalpressures than it otherwise could. Cooperating with container 13 is aheavy plunger 16 with its lower end formed to slidably tit the liner 15.A facing plate 17 of stainless steel is attached (as by spot welding) tothe end of the plunger. Parts 15 and 17 are preferably made of 309stainless steel (Z2-24% chrominum, 12-15% nickel, plus small amounts ofcarbon, manganese and silicon). Plunger 16 has a rod 18 which passesthrough a hole in closure plate 10 and through a stuing box 19 carriedby a water jacket 20 which rests on plate 10 and serves to cool thestuing box. The stuffing box 19 is packed with asbestos packing wellsaturated with high vacuum grease. Bolts 21 serve to secure plate 10 andwater jacket 20 to the top of the furnace tube 8, with air-tight jointsbetween the tube and the plate and the plate and water jacket.

The plunger rod 1S has its upper end connected byl coupling 22 to thelower end of rod Z3 of piston Ztl which is operatively mounted in fluidpower cylinder 25. The ycylinder is carried by a superstructurecomprising beam 26 and uprights 27 which connect the beam 26 to basemembers 6.

A graduated scale 28 is adjustably mounted on coupling 22 to move withplunger 16 and is arranged lto cooperate with xed pointer 29 supportedby the furnace tube 5. :Scale 28 thus arranged is adapted to indicatethe erably calibrated to indicate directly the volume of the liner forany position of the plate.

The portion of the furnace tube 8 extending above cover 4 of the furnaceis iitted with a water jacket 30 to .prevent the upper part of the tubefrom reaching unduly high temperatures. To indi-cate and control thetemperature of the treating ltube within the furnace chamber the furnaceis fitted with a radiation pyrorneter 31. As a check n the temperaturethe furnace may 4also be tted with an optical pyrometer (not shown).

5In the use of the heat treating apparatus for carrying out the methodof the present invention, the procedure may be varied in a number ofrespects, depending Vespecially upon the degree of purity specified forthe beryllium bodies to be produced, the density required for suchbodies and cost considerations. For purposes of explanation adescription will first be given of the procedure suitable for theproduction of beryllium bodies of predetermined form and size, of aspecilied density and a high degree of purity.

Preliminarily it may be noted that the invention allows of wide latitudeas to the size of the beryllium bodies produced. In fact the inventionhas made is possible to produce metallic beryllium bodies of maximumdensity and excellent physical properties far larger in size thananything heretofore reported. Also, in the practice of the invention,the forms of bodies produced may be varied, subject only to the obviousconditions that the container or die in which the body is sintered musthave its wall parts which cooperate with the pressure-applying plungerformed with inner surfaces parallel to the plunger movement. The bodiesmay be solid or tubular or other- 'wise recessed. For simplicity ofillustration the accompanying drawing shows apparatus for producingbodies of cylindrical form.

Assuming that bodies of beryllium to be produced are to be of a highdegree of purity and a density of 1.85, which is approximately thedensity of cast beryllium, that the container 13 and plunger 16 havebeen provided of desired form and size, and that the powdered berylliumfor use has been subjected to gross purification, as by the mechanicalcrushing and screening method above referred to, a charge of such powderis accurately weighed out corresponding to the density specified for thebody to be produced of known or computable volume, and is introducedinto the liner 15 and the latter lowered into container 14 resting inthe open furnace tube 8. With the power piston 24 held in its uppermostposition, the plunger 16 with parts 10, 19 and 20 assembled on rod 18,is lowered into the furnace tube and secured by coupling 22 to thepiston rod 23. This supports the plunger with its lower 'end above thetop opening of container 13.

The vacuum -pump is now started and operated until the pressure in thefurnace tube is reduced to 10 microns of mercury, or lower, and it isevident (from low rate of change in pressure) that the air iscorrespondingly exhausted from the powder charge. The evacuation of theheating tube should, of course, be at a suiciently slow rate to avoiddrawing powder from lcontainer 13. Exhausting to the vacuum pressurenoted may take from one to iiVe hours, depending upon the initial degreeof purity of the metallic powder and the size and shape of the body tobe produced.

Following the exhausting stage described the furnace is heated, whilethe `operation of the vacuum pump continues, until the temperature ofthe treating tube reaches about 900 C. During this stage gas andvaporizable impurities present in the charge are evolved 'and removed bythe pump. Such evolution of vapor may be accompanied, for a time, byincreased pressure in the treating tube. When the pressure is againfairly stable at l0 microns of mercury or lower, which may be afterheating from one to forty hours, pressure uid is Kadmitted to the top ofthe power cylinder to lower the plunger 16 and apply a low mechanicalpressure to the mass of powder, the operation of the Vacuum pumpmeanwhile continuing.

The mechanical pressure applied should be great enough to preventcontraction of the sintering mass away from the container walls but notgreat enough to distort the container, which may be weakened at therelatively high sintering temperature of beryllium. A pressure of '70pounds per square inch on the top of the charge has been found suitablefor this purpose. While higher pressures than this may be used, undulyhigh pressures during sintering are not only unnecessary but alsoobjectionable as they tend, by distortion of the container, to causeformation of -cracks in the sintered body and difliculty in separatingit from the container. As the sintering temperature of the berylliumvaries with its purity, the latter and also the character of theconstituent material of the container may aifect the maximum mechanicalpressure suitable for use. In any case the suitable pressure will be lowin comparison with compacting pressures commonly used in powdermetallurgy.

At the same time that mechanical pressure is applied to the chargeheating of the charge is increased until the container 13 is at atemperature sufficiently high to insure thorough sintering throughoutthe mass of the charge without unreasonably prolonging the treatment.This temperature will vary with the purity of the beryllium making upthe charge. With high purity assumed for the procedure being describedthe temperature should be carried to about 1125o C. Heating very farabove this temperature may cause pronounced grain growth and should beavoided because such growth would prevent attainment of the malleabilityand ductility which is `one of the objects of the invention. With lowerdegrees of purity the temperature at the sintering stage in question maybe as low as 1000 C.

The charge should be held under the specified mechanical pressure at thehigher sintering temperature until sintering is accomplished throughoutthe mass. During the heating of the charge under mechanical pressure theoperator observes the volume gauge 28 and when the gauge indicates acontainer volume which, according to prior computation, corresponds tothe density specified for the product, heat is turned off the furnaceand mechanical pressure on the charge is terminated by raising the powerpiston 24.

The operation of the vacuum pump is continued throughout the heating andpreferably, after the furnace burners are turned olf, during the coolingof furnace and charge.

When the container 13 has cooled to a temperature of blackness thefurnace tube is opened, the container lifted out and the charge dumpedout with the liner 15 possibly adhering to it, though making the linerof stainless steel minimizes such adherence. The liner is then peeledfrom the sintered body, being cut into several pieces if necessary, tofree it from the sintered mass. It will be understood that the use ofthe relatively thinwalled liner facilitates the carrying out of thetreatment because it prevents adherence of the sintering charge to themain walls of the container and facilitates compacting of the charge andits separation from the container.

By the use of sintering containers of suitable character a wide varietyof beryllium articles can be produced. For example, a toothed spur gearwheel of beryllium can be produced by using in place of container 13 ofFig. 1 a die such as is shown in Fig. 2. Here the die, indicatedgenerally by the numeral 32, comprises a female body 33 and acooperating male body 34, both parts preferably formed of stainlesssteel. In carrying out the process the beryllium powder is charged intodie body 33, the male member 34 inserted into the top of the die cavity,the assembly lowered into the furnace tube S and the latter closed withplunger 16 resting on top 0f die member 34. The further procedure maythen be as above described.

The die 33 may be so designed as to depth of its chamber that when asuitable weight of powder is charged into the die, compression of thecharge during the treatment will produce the nominal maximum density ofmetallic beryllium when the bottom of plunger 16 engages the top of diebody 33. Such compacting of the charge usually involves a reduction involume of about fifty percent. lf a lesser density is desired for thebody to be produced, the operator can readily achieve this by followingthe indication on scale 28 and stopping the application of pressure andheat to the charge at a suitable point to produce a predetermineddensity below the maximum.

In the last described procedure the stainless steel metal of the die inaddition to reducing adherence to the die of the sintered metal, has thefurther advantage that, up to the sintering temperatures of beryllium,the coefficients of thermal expansion of both metals are nearlyidentical; so that, on cooling, separation of the sintered body from thedie is facilitated and cracking of the sintered body by differentialcontraction of the die and sintered body is avoided. This feature ofsimilar coellcients of expansion is especially important in formingberyllium bodies having recessed surface contours with berylliumembracing or surrounding portions of the die, because most die material,other than stainless steel, suitable for use at the temperatures andpressures involved in the present process have coeflicients of expansionat such temperatures considerably less than that of beryllium, so thatparts of the beryllium structure embracing the die material aresubjected to shrinkage stresses caused by the greater contraction of theberyllium against the more slowly contracting die material.

Metallic beryllium bodies produced in the manner described are not onlycharacterized by a line-grained heterogeneous microscopic structure,predetermined density, high malleability, ease of machining andinsensitiveness to thermal shock, but also are marked by extremely highpurity of the constituent metallic beryllium. Itis believed that thehigh purity attained is to an important extent due to the evacuation ofthe container while the charge therein is in an uncompacted state. Thisapplies to the evacuation both before and during heating of the charge.With the charge in this state the evacuation with the pump beforeheating and in the early stages of the heating more effectively removeswater vapor and oxidizing gases from the charge so that oxidation of thecharge in the later heating stage is largely prevented. The uncompactedstate of the charge during vaporization of impurities also favors a morecomplete removal of such impurities by the vacuum pump. Also, it shouldnot be overlooked that minimizing of oxide formation in the chargecorrespondingly favors sintering and high strength of the integratedbody. ln addition, the removal from the nely divided charge or" gasesand impurities in vapor form is an important factor securing freedomfrom porosity and permitting accurate and reliable determination ofdensity of the sintered body.

The applications of vacuum, sintering heat and low mechanical pressurewhich characterize the present method has the further great advantage,already briefly noted in the foregoing description, that it makespossible the production of a metal such as beryllium in extremely largebodies having excellent physical properties including fine grainstructure, good malleability, ductility, and machinability, goodresistance to temperature shock and full density. It is believed thatthese physical properties are at least in part essentially due to theprolonged treatment by evacuation and heating which strips from theinterstices and pores of the metal mass all vaporizable material so thatit is possible for the moderate mechanical pressure applied to thesoftening mass to more elfectively consolidate the metal to its fulldensity. It will be appreciated that in the production even of smallbodies the stripping action referred to in its very nature requires aconsiderable amount of time and, furthermore, that the time mustincrease with the size of the metal mass under treatment. It will alsobe appreciated that the prolonged time of treatment is an essentialfeature of the method regardless of the degree of purity of the powderedmetal to which the treatment is applied, since it is practicallyimpossible in the handling of the metallic powder to avoid adsorption ofoxidizing gases and vapors on the surfaces of the powder particles, andas the powder material is consolidated under pressure these adsorbedmaterials line the resulting pores in the mass and, together with anyother vaporizable impurities that may be present in the material of thecharge, must be removed in order to attain the desired density under themoderate mechanical pressures that characterize the method.

As already noted, considerable variation of the procedure followed andof the construction of the apparatus used is possible in practice of thepresent improvements. For example, if the density of the product is notcritical and the highest degree of purity unnecessary a less completeevacuation of the charge container is permissible. This will shorten thetime of the evacuation treatment prior to heating or during heating orboth.

Other variations permissible in particular cases will be apparent fromthe nature of the treatment and the considerations indicated by theforegoing description.

Accordingly, both as to the method of procedure and the apparatusemployed, it will be understood that the invention is not limited to thespecific disclosure but may be Varied within the bounds of equivalencyand the terms of the appended claims.

What is claimed is:

1. In a method of producing malleable bodies of metallic beryllium, thesteps of charging a mass of the metal in a finely divided state suitablefor powder metallurgy purposes into a container with an interior havingthe form of the body to be produced; subjecting the interior of thecontainer and the charge therein to the combined action of evacuationand heating at a temperature below about 900 C. until a large part ofany gas and Vapor sorbed in the charge has been removed therefrom asevidenced by the pressure in the container; thereafter, whilemaintaining the evacuation of the container, subjecting it and thecharge to sintering heat within the temperature range from about l0O0 C.upward to a temperature below that at which pronounced grain growth ofthe beryllium treated would occur and prolonging the heating at suchsintering temperature until the charge is sintered throughout; duringthe prolonged combined evacuating and heating treatment in the statedsintering temperature range subjecting the charge to mechanical pressuregreat enough to maintain the sintering charge in contact with thecontainer walls but both insulicient to cause distortion of the heatedcontainer and much lower than would be required, in the absence of saidevacuation, to produce the same density of the charge; and separatingthe container from the sintered body so formed.

2. The method of claim l in which the charge is subjected to amechanical pressure of about 70 pounds per square inch during theevacuating and heating treatment thereof at the sintering temperature.

3. The method of claim l in which the finely divided metal is chargedinto a container having a thick-walled outer structure and a separablethin-walled liner fitting the inner surfaces of the outer structure andthe container is separated from the sintered charge by first removingthe liner and sintered charge from the outer structure and thenstripping the liner from the sintered charge.

4. In a method of producing malleable bodies of metallic beryllium, thesteps of charging a mass of the metal in a finely divided state suitablefor powder metallurgy purposes into a container with an interior havingthe form of the body to be produced; subjecting the interior of thecontainer and the charge therein to the combined action of evacuationand heating at a temperature below about 900 C. until a large part ofany gas and vapor sorbed in the charge has been removed therefrom asevidenced by the pressure in the container; thereafter, whilemaintaining the evacuation of the container, heating it and the chargeto a sintering temperature within the range from about 1000 C. to about1125c C. and prolonging the heating at such sintering temperature untilthe charge is sintered throughout; during the prolonged combinedevacuating and heating treatment in the stated sintering temperaturerange subjecting the charge to mechanical pressure great enough tomaintain the sintering charge in contact with the container walls butboth insufiicient to cause distortion of the heated container and muchlower than would be required, in the absence of said evacuation, toproduce the same density of the charge; and separating the containerfrom the sintered Vbody so formed.

5. The method of claim 4 in which the charge is subjected to amechanical pressure of about 70 pounds per square inch during theevacuating and heating treatment thereof at the sintering temperature.

6. The method of claim 4 in which the rinely divided metal is chargedinto a container having a thick-walled outer structure and a separablethin-walled liner fitting the inner surfaces of the outer structure andthe container is separated from the sintered charge by first removingthe liner and sintered charge from the outer structure and thenstripping the liner from the sintered charge.

7. In a method of producing malleable bodies of metallic berylliumhaving recessed surface contours the steps of charging a mass of themetal in a finely divided state suitable for powder metallurgy purposesinto a charnbered die of stainless steel having its chamber Walls shapedto form the recessed surfaces of the beryllium body to be produced;subjecting the chambered die and the charge therein to the combinedaction of evacuation and heating at a temperature below about 900 C.until a large part of any gas and vapor adsorbed in the charge has beenremoved therefrom as evidenced by the pressure in the die chamber;thereafter7 while maintaining the evacuation of the die chamber,subjecting the die and the charge to sintering heat within thetemperature range from about 1000 C. upward to a temperature below thatat which pronounced grain growth of the beryllium treated would occurand prolonging the heating at such sintering Cil temperature until thecharge is sintered throughout; during the prolonged combined evacuatingand heating treat ment in the stated sintering temperature rangesubjecting the charge to mechanical pressure great enough to main.- tainthe sintering charge in Contact with the chamber walls of the die butboth insuiiicient to cause distortion of the said Walls and much lowerthan would be required, in the absence of said evacuation, to producethe same density of the charge; and separating the die from the sinteredbody so formed.

8. In a method of producing malleable bodies of metallic beryllium inwhich a mass of the metal in a inely divided state suitable for powdermetallurgy purposes is charged into a container with an interior havingthe form of the body to be produced, the steps of simultaneouslysubjecting the container and the charge therein to prolonged andeffective evacuation and sintering heat within the temperature rangefrom about 1000 C. upward to a temperature below that at whichpronounced grain growth of the beryllium treated would occur andprolonging the heating at such sintering temperature until the charge issintered throughout; and during the prolonged combined evacuating andheating treatment in the stated sintering temperature range subjectingthe charge to mechanical pressure great enough to maintain the sinten'ngcharge in contact with the container walls but insufficient to causedistortion of the heated container.

References Cited in the 'ile of this patent UNITED STATES PATENTS1,698,300 Ehlers Jan. 8, 1929 1,766,865 Williams June 24, 1930 1,896,853Taylor Feb. 7, 1933 2,206,395 Gertler July 2, 1940 2,549,596 HamiltonApr. 17, 1951 2,653,494 Greutz Sept. 29, 1953 2,725,288 Dodds et al.Nov. 29, 1955 FOREIGN PATENTS 508,028 Great Britain June 23, 1939523,318 Great Britain July 11, 1940 704,517 Germany Apr. 1, 1941 OTHERREFERENCES Clark: Colorado School of Mines Quarterly, vol. 36

No. 4, Oct. 1941, p. 48.

Wolff: Powder Metallurgy, pub. by American Soc. for Metals, Cleveland,Ohio, 1942, pp. lOl-103, 396.

1. IN A METHOD OF PRODUCING MALLEABLE BODIES OF METALLIC BERYLLIUM, THESTEPS OF CHARGING A MASS OF THE METAL IN A FINELY DIVIDED STATE SUITABLEFOR POWER METALLURGY PURPOSES INTO A CONTAINER WITH AN INTERIOR HAVINGTHE FORM OF THE BODY TO BE PRODUCED; SUBJECTING THE INTERIOR OF THECONTAINER AND THE CHARGE THEREIN TO THE COMBINED ACTION OF EVACUATIONAND THE CHARGE THEREIN TO THE COMBINED ABOUT 900*C. UNTIL A LARGE PARTOF ANY GAS AND VAPOR SORBED IN THE CHARGE HAS BEEN REMOVED THEREFROM ASEVIDENCED BY THE PRESSURE IN THE CONTAINER; THEREAFTER, WHILEMAINTAINING THE EVACUATION OF THE CONTAINER, SUBJECTING IT AND THECHARGE TO SINTERING HEAT WITHIN THE TEMPERATURE RANGE FROM ABOUT 1000*C.UPWARD TO A TEMPERATURE BELOW THAT AT WHICH PRONOUNCED GRAIN GROWTH OFTHE BERYLLIUM TREATED WOULD OCCUR AND PROLONGING THE HEATING AT SUCHSINTERING TEMPERATURE UNTIL THE CHARGE IS SINTERED THROUGHOUT; DURINGTHE PROLONGED COMBINED EVACUATING AND HEATING TREATMENT IN THE STATEDSINTERING TEMPERATURE RANGE SUBJECTING THE CHARGE TO MECHANICAL PRESSUREGREAT ENOUGH TO MAINTAIN THE SINTERING CHARGE IN CONTACT WITH THECONTAINER WALLS BUT BOTH INSUFFICIENT TO CAUSE DISTORTION OF THE HEATEDCONTAINER AND MUCH LOWER THAN WOULD BE REQUIRED, IN THE ABSENCE OF SAIDEVACUATION, TO PRODUCE THE SAME DENSITY OF THE CHARGE; AND SEPARATINGTHE CONTAINER FROM THE SINTERED BODY SO FORMED.